Capacitive touch panel having dual resistive layer

ABSTRACT

A patterned substrate for a touch screen sensor assembly that includes a plurality of electrodes that are formed from a first transparent conductive layer that has a first surface resistivity. The substrate also has a plurality of traces that may be used to couple the electrodes controller associated with the touch screen sensor assembly. The traces are formed from a second conductive layer that has a second surface resistivity that is less than the surface resistivity of the first conductive layer. The first and second conductive layers may be formed from indium tin oxide (ITO) having different surface resistivities. A second, similarly configured substrate can be provided and may be spaced apart from the first substrate by a dielectric spacer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/629,705, entitled:

“CAPACITIVE TOUCH PANEL HAVING DUAL RESISTIVE LAYER,” filed on Dec. 2,2009, and now U.S. Pat. No. 8,209,861, which claims priority under 35U.S.C. 119 to U.S. Provisional Application No. 61/120,254, entitled:“CAPACITIVE TOUCH PANEL HAVING DUAL RESISTIVE LAYER,”filed on Dec. 5,2008, all the contents of which are incorporated herein as if set forthin full.

BACKGROUND

As computers and other electronic devices become more popular,touch-sensing systems are becoming more prevalent as a means forinputting data. For example, touch-sensing systems can be found inautomatic teller machines, personal digital assistants, casino gamemachines, mobile phones, and numerous other applications.

Capacitive touch sensing is one of the most widely used techniques intouch screen industries. Capacitive touch sensors are mainly divided intwo groups, namely, continuous capacitive sensors and discontinuous(patterned) capacitive sensors. In a continuous capacitive sensor, thesensor includes a sheet of conducting thin film that is electricallyexcited from four corners of the touch screen. The signals induced by auser's touch are transmitted from the four corners to a controller,where they are decoded and translated into coordinates. In a typicalpatterned capacitive touch screen, the sensor may include one or moreseries of parallel conductive bars that are driven from one or both endswith excitation signals from a controller coupled to the conductive barsby lead lines. The signals induced by a user's touch may be transmittedto the controller with the same lead lines that excite the sensor bars.These signals may then be decoded in the controller and the touchcoordinates may be reported to a computer.

Touch sensors utilizing more than one patterned sensing layer are oftenused to determine the coordinates of a touch with high accuracy,provided that the sensing layers have a suitable pattern geometry. Oneexample of a touch screen assembly 10 that includes two patternedconductive layers 12 and 14 is shown in FIG. 1A and FIG. 1B. Thepatterned conductive layers 12 and 14 may be made from a transparentconductive material, such as indium tin oxide (ITO), and each layer isgenerally disposed on a transparent substrate (not shown here). Each rowof conductive elements of each of the sensor layers 12 and 14 includes aseries of diamond-shaped electrodes that are connected to each otherwith short strips of relatively narrow rectangles. A dielectric layer 16separates the two conductive layers 12 and 14, and serves to preventthem from coming into direct contact with each other. As an example thedielectric layer 16 may include an adhesive manufactured from anynon-conductive, transparent material.

As shown, the end of each row of the two patterned conductive layers 12and 14 is coupled to one of a set of traces 18 (e.g., silver traces)that are in turn coupled to a controller 20. Generally, the traces 18are used to couple the electrodes to the controller 20 because theresistance of the ITO conductive layer is relatively high. Theresistance of the ITO conductive layer is relatively high because theamount of conductive material used in the ITO compound is keptrelatively low so that the layer is substantially transparent. Thetraces 18 may generally be deposited on to the substrate using anysuitable process. One method includes vacuum sputtering a metal layer(e.g., aluminum or Mo—Al—Mo) onto the substrate, then etching the traces18 using a photo etching process. Another method includes silk-screenprinting silver conductive ink to form the traces 18.

The controller 20 may include circuitry for providing excitationcurrents to the capacitive sensors 12 and 14 and for detecting signalsgenerated by the sensors. Further, the controller 20 may include logicfor processing the signals and conveying touch information to anotherpart of an electronic device, such as a processor.

FIG. 2 illustrates the various layers that may be included in a touchscreen sensor assembly 40. The assembly 40 includes a top substrate 42 aand a bottom substrate 42 b that are each coated with patterned ITOlayers 44 a and 44 b, respectively, that include a plurality ofelectrodes. The substrates 42 a and 42 b may be configured from anysuitable transparent material, including glass, plastic (e.g., PET), orthe like. Further, the top ITO layer 44 a may be separated from thebottom ITO layer 44 b by a suitable dielectric spacer 48 that is adheredby optically clear adhesive layers 46 a and 46 b.

As discussed above, the ITO layers 44 a and 44 b may be coupled to oneor more controllers that are operable to excite and sense electricalsignals on the electrodes of the ITO layers 44 a and 44 b. Toelectrically connect the controller to the ITO layers 44 a and 44 b, aflexible printed circuit (FPC) 56 may be coupled to the assembly 40. TheFPC 56 may include an FPC substrate 55, top copper traces 54 a, andbottom copper traces 54 b that are used to couple the top and bottom ITOlayers 44 a and 44 b to a controller. To make the connection between thecopper traces 54 a and 54 b and the ITO layers 44 a and 44 b, traces 50a and 50 b may be disposed in contact with portions of the ITO layers.Further, the traces 50 a and 50 b may be coupled to the copper traces 54a and 54 b using electrically conducive adhesive layers 52 a and 52 b,which may, for example, include an anisotropic conductive adhesive(ACA).

SUMMARY

The following embodiments and aspects of thereof are described andillustrated in conjunction with systems, tools, and methods which aremeant to be exemplary and illustrative, and not limiting in scope. Invarious embodiments, one or more of the above-described problems havebeen reduced or eliminated, while other embodiments are directed toother improvements.

According to a first aspect, a patterned substrate for use in a touchscreen sensor assembly is provided. The patterned substrate includes asubstrate and a first non-metallic conductive layer disposed on thesubstrate, the first non-metallic conductive layer forming a pattern ofelectrodes. The patterned substrate also includes a second non-metallicconductive layer disposed on the substrate, the second non-metallicconductive layer forming a pattern of traces that are each electricallycoupled to at least one of the electrodes. In addition, the secondnon-metallic conductive layer has a surface resistivity that is lessthan the first non-metallic conductive layer.

According to a second aspect, a method for manufacturing a patternedsubstrate for a touch screen sensor assembly is provided. The methodincludes providing a substrate, and depositing a first non-metallicconductive layer onto the substrate, wherein the first non-metallicconductive layer has a surface resistivity. The method also includesremoving the first non-metallic conductive layer from the substrate in aviewing portion of the substrate, wherein the viewing portioncorresponds to an area of the substrate that is to be aligned with adisplay when the patterned substrate is configured as part of a touchscreen sensor assembly. The method further includes depositing a secondnon-metallic conductive layer onto the viewing portion of the substrate,wherein the second non-metallic conductive layer has a surfaceresistivity that is higher than that of the first non-metallicconductive layer. Additionally, the method includes removing portions ofthe second non-metallic conductive layer to form a pattern ofelectrodes, and removing portions of the first non-metallic conductivelayer to form a plurality of traces, wherein each trace is electricallycoupled to at least one electrode.

According to a third aspect, a touch screen sensor assembly is providedthat includes first and second substrates disposed in parallel with eachother with a space therebetween. Each of the first and second substratesincludes a first non-metallic conductive layer disposed on thesubstrate, the first non-metallic conductive layer forming a pattern ofelectrodes. Each of the first and second substrates also includes asecond non-metallic conductive layer disposed on the substrate, thesecond non-metallic conductive layer forming a pattern of traces thatare each electrically coupled to at least one of the electrodes.Further, the second non-metallic conductive layer has a surfaceresistivity that is less than the first non-metallic conductive layer.

According to a fourth aspect, a patterned substrate for use in a touchscreen sensor assembly is provided. The patterned substrate includes asubstrate and a first ITO layer disposed on the substrate, the first ITOlayer forming a pattern of electrodes. The patterned substrate alsoincludes a second ITO layer disposed on the substrate, the second ITOlayer forming a pattern of traces that are each electrically coupled toat least one of the electrodes. Additionally, the second ITO layer has asurface resistivity that is less than that of the first ITO layer.

According to a fifth aspect, a method for manufacturing a touch screensensor assembly is provided. The method includes providing a firsttransparent substrate and depositing a first non-metallic conductivelayer onto the first transparent substrate, wherein the firstnon-metallic conductive layer has a surface resistivity. The method alsoincludes removing the first non-metallic conductive layer from the firsttransparent substrate in a viewing portion of the first transparentsubstrate, wherein the viewing portion corresponds to an area of thefirst transparent substrate that is to be aligned with a display. Themethod further includes depositing a second non-metallic conductivelayer onto the viewing portion of the first transparent substrate,wherein the second non-metallic conductive layer has a surfaceresistivity that is higher than that of the first non-metallicconductive layer. The method also includes removing portions of thesecond non-metallic conductive layer from the first transparentsubstrate to form a first pattern of electrodes, and removing portionsof the first non-metallic conductive layer from the first transparentsubstrate to form a plurality of traces. Additionally, the methodincludes providing a second transparent substrate, and depositing athird non-metallic conductive layer onto the viewing portion of thesecond transparent substrate, wherein the third non-metallic conductivelayer has a surface resistivity that is substantially equal to that ofthe second non-metallic conductive layer. Further, the method includesremoving portions of the third non-metallic conductive layer from thesecond transparent substrate to form a second pattern of electrodes, andbonding the first transparent substrate to the second transparentsubstrate using an optically clear adhesive. In addition, each trace onthe first transparent substrate formed from the first non-metallicconductive layer is electrically coupled to at least one electrode ofeither the first pattern of electrodes or the second pattern ofelectrodes.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a top view and cross-sectional view of aprior art capacitive touch sensor assembly.

FIG. 2 illustrates the configuration of various layers for a prior arttouch screen sensor assembly.

FIG. 3 illustrates an automatic teller machine that incorporates anexemplary touch screen assembly.

FIG. 4 illustrates an electronic device that incorporates an exemplarytouch screen sensor assembly.

FIGS. 5-8 illustrate process steps for manufacturing an exemplary touchscreen sensor assembly.

FIG. 9 illustrates the configuration of various layers for an exemplarytouch screen sensor assembly.

FIGS. 10A-H illustrate an exemplary manufacturing process for a touchscreen sensor assembly.

DETAILED DESCRIPTION

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that it is not intended to limit the inventionto the particular form disclosed, but rather, the invention is to coverall modifications, equivalents, and alternatives falling within thescope and spirit of the invention as defined by the claims.

FIGS. 3 and 4 illustrate an automatic teller machine (ATM) 60 thatincorporates an exemplary touch screen sensor assembly 62. Although theATM 60 is illustrated, the embodiments described herein may beincorporated into any electronic device that includes a touch screen,such as a personal digital assistant (PDA), a casino game machine, amobile phone, a computer, a voting machine, or any other electronicdevice. The touch screen sensor assembly 62 may include two layers oftransparent patterned conductive material (may also be called“resistive” material), such as a non-metallic ceramic like ITO, that aredisposed on two substrates positioned in a spaced, parallel relationship(see FIG. 9). The touch screen sensor assembly 62 may also be coupled tocontrol logic 66 (shown in FIG. 3) that is operable to excite theconductive material and to sense touches on or near the touch screensensor assembly 62. As an example, the control logic 66 may include acommercial touch screen controller (e.g., a controller provided byCypress Semiconductor, Analog Devices, Atmel, Synaptics, and others), anapplication specific integrated circuit (ASIC), or any other suitablecontroller. Further, the touch sensor assembly 62 may overlay a display64 (shown in FIG. 3), which may be any type of display, such as an LCDdisplay.

FIGS. 5-8 illustrate top views of an ITO patterned substrate 70 invarious sequential stages of an exemplary manufacturing process. Thesubstrate 70 may be included in a touch screen sensor assembly (e.g.,the touch screen sensor assembly 62 shown in FIGS. 3-4). ThroughoutFIGS. 5-8, similar or identical elements are indicated by the samereference numerals.

FIG. 5 shows the substrate 70 after it has been coated with an ITO layer72 that has a relatively low surface resistivity (e.g., less than 20Ohms, less than 10 Ohms, or the like). The ITO layer 72 may be depositedonto the substrate 70 using any suitable process, such as vacuumsputtering. Although the ITO layer 72 is shown to be opaque, this isgenerally for illustrative purposes and it should be appreciated thatthe layer 72 may be somewhat transparent. The substrate may be formedfrom any suitable material, including glass, plastic (e.g., PET), orother material.

FIG. 6 illustrates the next step in the manufacturing process, which isto remove (e.g., by photo etching) the lower resistance ITO layer 72 offthe portion of the substrate 70 that will overlay a display (indicatedby the arrow 74). A section of the ITO layer 72 is retained along one ormore edges of the substrate 70 that will not overlay the display, and isused in a later step to form traces that function to couple the ITOelectrodes to a controller. Although only a strip of the ITO layer 72 isretained in FIG. 6, it should be appreciated that the ITO layer 72 maybe retained wherever it may be desirable to form conductive traces onthe substrate 70. Further, the low resistance ITO layer 72 may not beused in the viewing area because its transparency may be too low, suchthat the layer 72 would obstruct the view of an underlying display.

FIG. 7 illustrates the next step in the manufacturing process, which isto deposit (e.g., by vacuum sputtering) a relatively higher resistanceITO layer 76 onto the viewing portion of the substrate 70. As anon-limiting example, the ITO layer 76 may have a surface resistivity ofabout 50 Ohms, 100 Ohms, 200 Ohms, or the like. The ITO layer 76 may berelatively transparent, so that the view of a display associated with anassembled touch screen that includes the substrate 70 will not beobstructed.

FIG. 8 shows the substrate 70 after the next step in the manufacturingprocess, wherein a pattern of electrodes has been formed by etching(e.g., photo etching) the higher resistivity ITO layer 76, and traceshave been formed by etching the lower resistivity ITO layer 72. In thisregard, the electrodes formed by the ITO layer 76 may be coupled to acontroller by the traces formed by the ITO layer 72, whichadvantageously eliminates the need for metal traces. It should beappreciated that FIG. 8 illustrates one example of a pattern ofelectrodes and traces, and that the manufacturing process describedherein may be used to produce a substrate with any suitable pattern ofelectrodes and traces.

FIG. 9 illustrates the various layers that may be included in anexemplary touch screen sensor assembly 80. The assembly 80 includes atop substrate 82 a and a bottom substrate 82 b that are each coated withrelatively high resistance ITO layers 84 a and 84 b (labeled ITO1),respectively, that include a plurality of electrodes. The substrates 82a and 82 b may be configured from any suitable transparent material,including glass, plastic (e.g., PET), or the like. Further, the top ITOlayer 84 a may be separated from the bottom ITO layer 84 b by a suitabledielectric spacer 88 that is adhered by optically clear adhesive layers86 a and 86 b.

As discussed above, the ITO layers 84 a and 84 b may be coupled to oneor more controllers that are operable to excite and sense electricalsignals on the electrodes of the ITO layers 84 a and 84 b. Toelectrically connect the controller to the ITO layers 84 a and 84 b, aflexible printed circuit (FPC) 96 may be coupled to the assembly 80. TheFPC 96 may include an FPC substrate 95, top copper traces 94 a, andbottom copper traces 94 b, that are used to couple the top and bottomITO layers 84 a and 84 b, respectively, to a controller. To make theconnection between the copper traces 94 a and 94 b and the ITO layers 84a and 84 b, lower resistance ITO layers 90 a and 90 b (labeled ITO2) maybe disposed in contact with portions of the ITO layers 84 a and 84 b.Further, the lower resistance ITO layers 90 a and 90 b may be coupled tothe copper traces 94 a and 94 b using electrically conductive adhesivelayers 92 a and 92 b, which may, for example, include an anisotropicconductive adhesive (ACA). It is noted that one reason the lowerresistance ITO layers 90 a-b are used for connection to the coppertraces 94 a-b, as opposed to the higher resistance ITO layers 84 a-b, isthat it may be desirable that the trace widths be relatively narrow, asnarrow trace widths reduce the area required for the traces, and mayalso reduce the undesirable capacitance present in the traces. At thedesirable trace widths, the relatively transparent ITO layer 84 may havea high resistance, which would greatly reduce the performance of thetouch screen sensor.

FIGS. 10A-H illustrate an exemplary manufacturing process for a touchscreen sensor assembly including ITO layers having two differentresistivities. For example, the process may be used to manufacture thetouch screen sensor assembly 62 shown in FIGS. 3 and 4. As shown in FIG.10A, the touch screen sensor assembly may include a bottom substrate 100constructed from a suitable transparent material (e.g., glass, PET, orthe like). The bottom substrate 100 may be coated with a layer 102 ofITO (or other suitable material) having a relatively low resistivity(e.g., 50 Ohms/square, or the like) using a deposition process such asvacuum sputtering.

Next, as shown in FIG. 10B, the low resistivity ITO layer 102 may beetched away from a viewing portion 104 of the bottom substrate 100. Theetching may be performed by any suitable layer removal process, such asphoto etching, or the like.

Once the low resistivity ITO layer 102 has been etched away from theviewing portion 104 of the bottom substrate 100, a high resistivity ITOlayer 106 may be deposited onto the viewing portion 104 of the bottomsubstrate 100, as shown in FIG. 10C. In a similar step shown in FIG.10D, a high resistivity ITO layer 122 may be deposited onto a topsubstrate 120. As can be appreciated, the high resistivity ITO layers106 and 122 may be more transparent than the low resistivity ITO layer102, such that a user may view a display that resides behind the viewingportion 104 of the assembled touch screen sensor assembly.

FIG. 10E illustrates the result after an etching process, wherein thehigh resistitivity ITO layer 106 has been etched into a pattern ofelectrodes. Further, the low resistitivity ITO layer 102 has been etchedinto a pattern of traces outside of the viewing portion 104 of thebottom substrate 100. The pattern of traces etched from the lowresistivity ITO layer 102 includes a plurality of traces 103 andconnection points 108 that are coupleable to electrodes formed by thehigh resistivity ITO layer 122 of the top substrate 120 when the touchscreen sensor is assembled. Further, the traces etched from the ITOlayer 102 include a portion 110 that operates to couple a connector tothe traces (see FIG. 10H) so that the touch screen sensor may beconnected to a controller and/or a computer system. Similarly, FIG. 10Fillustrates the result after the high resistivity ITO layer 122 has beenetched into a pattern of electrodes on the top substrate 120.

FIG. 10G illustrates the result after the bottom substrate 100 and thetop substrate 120 have been laminated together using a suitableoptically clear adhesive (OCA). As shown, the “rows” of electrodesformed from the ITO layer 106 and the “columns” of electrodes formedfrom the ITO layer 122 are aligned with each other to form a diamondpattern of electrodes that substantially covers the viewing portion ofthe touch screen sensor assembly. Further, as noted above, theelectrodes formed from the ITO layer 122 of the top substrate 120 arecoupled to the traces 103 via the connection points 108, such that thetraces formed from the low resistivity ITO layer 102 may operate tocouple the electrodes from both the top substrate 120 and the bottomsubstrate 100 to a controller and/or a computer system.

FIG. 10H illustrates the touch screen sensor assembly after a connector130 (e.g., a flexible printed circuit connector) has been bonded to thebottom substrate 100 such that the traces formed from the ITO layer 102are coupled to contacts of the connector 130. The connector 130 may bebonded to the bottom substrate 100 using any suitable adhesive, such asan anisotropic conductive film (ACF) or adhesive.

The features described herein offer several advantages over previousdesigns. For example, in the case where metal traces are used, themanufacturing costs and complexity are high and environmental pollutionmay be a considerable problem. As another example, when silverconductive ink is printed for the traces, the trace height may berelatively large (e.g., greater than 10 um), the trace width must berelatively wide (e.g., greater than about 40 mm), and printingtolerances may be relatively large. Generally, a large trace height cancause unwanted bubbles to be formed when the top and bottom substratesare assembled together. By using a relatively low resistance ITO layerfor the traces, the above-noted shortcomings are reduced or eliminated.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and description isto be considered as exemplary and not restrictive in character. Forexample, certain embodiments described hereinabove may be combinablewith other described embodiments and/or arranged in other ways (e.g.,process elements may be performed in other sequences). Accordingly, itshould be understood that only the preferred embodiment and variantsthereof have been shown and described and that all changes andmodifications that come within the spirit of the invention are desiredto be protected.

We claim:
 1. A patterned substrate for use in a capacitive touch screen sensor assembly, the patterned substrate comprising; a substrate; a first non-metallic conductive layer disposed on the substrate, the first non-metallic conductive layer forming a pattern of electrodes; and a second non-metallic conductive layer disposed on the substrate, the second non-metallic conductive layer forming a pattern of traces that are each electrically coupled to at least one of the electrodes; wherein the second non-metallic conductive layer has a surface resistivity that is less than that of the first non-metallic conductive layer, and wherein the second non-metallic conductive layer has a surface resistivity of less than 20 ohms; and a flexible printed circuit (FPC) including an FPC substrate and a plurality of traces on a surface of the FPC substrate that are electrically coupled to the traces of the substrate formed by the second non-metallic conductive layer.
 2. The patterned substrate of claim 1, wherein the second non-metallic conductive layer includes indium tin oxide.
 3. The patterned substrate of claim 1, wherein the substrate is formed from a plastic material.
 4. The patterned substrate of claim 1, wherein the substrate is formed from a glass material.
 5. The patterned substrate of claim 1, wherein the first non-metallic conductive layer and the second non-metallic conductive layer include indium tin oxide.
 6. The patterned substrate of claim 1, wherein the first non-metallic conductive layer is disposed in a viewing portion of the substrate, wherein the viewing portion corresponds to an area of the substrate that is to be aligned with a display when the patterned substrate is configured as part of a touch screen sensor assembly, and wherein the second non-metallic conductive layer is on a portion of the substrate that does not include the viewing portion.
 7. A capacitive touch screen sensor assembly, comprising: first and second substrates disposed in parallel with each other with a space therebetween, each of the first and second substrates including: a first non-metallic conductive layer disposed on the substrate, the first non-metallic conductive layer forming a pattern of electrodes; and a second non-metallic conductive layer disposed on the substrate, the second non-metallic conductive layer forming a pattern of traces that are each electrically coupled to at least one of the electrodes, wherein the second non-metallic conductive layer has a surface resistivity that is less than that of the first non-metallic conductive layer, and wherein contact of an object over one of the first and second substrates causes a capacitive change between the first non-metallic conductive layers of the first and second substrates; and a flexible printed circuit (FPC) including an FPC substrate, a first plurality of traces on a first surface of the FPC substrate that are electrically coupled to the traces of the first substrate formed by the second non-metallic conductive layer, and a second plurality of traces on an opposed second surface of the FPC substrate that are electrically coupled to the traces of the second substrate formed by the second non-metallic conductive layer.
 8. The touch screen sensor assembly of claim 7, wherein the second non-metallic conductive layer disposed on the first and second substrates includes indium tin oxide.
 9. The touch screen sensor assembly of claim 7, further comprising: a first electrically conductive adhesive layer disposed between a first set of the plurality of traces of the FPC and traces of the first substrate; and a second electrically conductive adhesive layer disposed between a second set of the plurality of traces of the FPC and traces of the second substrate.
 10. The touch screen sensor assembly of claim 7, wherein each of the first and second substrates further include an optically clear adhesive layer disposed over the first non-metallic conductive layer.
 11. The touch screen sensor assembly of claim 7, wherein the first and second substrates are separated by a dielectric adhesive layer.
 12. The touch screen sensor assembly of claim 7, wherein, for each of the first and second substrates, the first and second non-metallic conductive layers are disposed in substantially the same plane.
 13. The touch screen sensor assembly of claim 7, wherein, for each of the first and second substrates, the first non-metallic conductive layer is disposed in a viewing portion of the substrate, wherein the viewing portion corresponds to an area of the substrate that is to be aligned with a display, and wherein the second non-metallic conductive layer is disposed on a portion of the substrate that does not include the viewing portion.
 14. The touch screen sensor assembly of claim 7, wherein the second non-metallic conductive layer has a surface resistivity of less than 20 ohms.
 15. The touch screen sensor assembly of claim 9, wherein the first and second electrically conductive adhesive layers include an anisotropic conductive adhesive (ACA).
 16. A touch screen sensor assembly, comprising: first and second substrates disposed in parallel with each other with a space therebetween, each of the first and second substrates including: a first non-metallic conductive layer disposed on the substrate, the first non-metallic conductive layer forming a pattern of electrodes; and a second non-metallic conductive layer disposed on the substrate, the second non-metallic conductive layer forming a pattern of traces that are each electrically coupled to at least one of the electrodes, wherein the second non-metallic conductive layer has a surface resistivity that is less than that of the first non-metallic conductive layer; a dielectric adhesive layer separating the first and second substrates; and a flexible printed circuit (FPC) including an FPC substrate, a first plurality of traces on a first surface of the FPC substrate that are electrically coupled to the traces of the first substrate formed by the second non-metallic conductive layer, and a second plurality of traces on an opposed second surface of the FPC substrate that are electrically coupled to the traces of the second substrate formed by the second non-metallic conductive layer. 